In recent years, a running control apparatus for an automobile which is equipped with a following distance control device has been developed and put into practical use, so as to enable the vehicle to follow or track a preceding vehicle, thereby to reduce the effort of the driver in a driving the automobile.
The running control apparatus equipped with the following distance control device is adapted to detect a following distance between the vehicle (hereinafter referred to as subject vehicle) and the preceding vehicle, based on information obtained from a forward recognition sensor, such as a camera and a laser radar, and control the vehicle speed by adjusting the engine output, or the like, so that the following distance becomes equal to a predetermined target following distance. The subject vehicle follows or tracks the preceding vehicle at the speed controlled in this manner.
Recently, there has been also proposed an apparatus that enables the subject vehicle to be decelerated by automatically actuating or operating a brake system when the preceding vehicle is decelerated, as disclosed in Japanese laid-open Patent Publication No. 7-65297.
In the apparatus disclosed in the above-identified publication, the speed of the subject vehicle is automatically reduced, namely, brakes are automatically applied to the subject vehicle, even where the preceding vehicle is decelerated by a large degree. Although the subject vehicle may be completely automatically braked or decelerated in accordance with the deceleration degree of the preceding vehicle, the resulting braking state of the vehicle does not always meet with the driver's intention. If the automatic braking does not meet with the driver's intention, the driver or other passenger of the vehicle may feel uncomfortable or disagreeable.
In the case where the vehicle needs to be decelerated by a large deceleration degree, therefore, it has been proposed to allow the driver to operate a brake pedal, namely, perform a normal braking action according to the driver's intention even during tracking running control. However, the operation of the brake pedal by the driver tends to be delayed, in view of the response of the driver to the deceleration of the preceding vehicle, namely, the time required for the driver to start operating the brake pedal, and it is thus necessary to provide a certain margin or excess time before the brake pedal is actually operated by the driver.